Method of carbonizing ferrous metal



Patented Mar. 6, 1934 1,50,116

METHOD OF CARBONIZING FERROUS METAL John H. Kyte, Fanwood, N. .L, assignor to Swedish Iron & Steel Corporation, New York, N. Y., a corporation of New York ,No Drawing. Application November 8, 1932, Serial No. 641,740

4 Claims. (Cl. 14817) This invention relates to the treatment of ferpears to cease. The invention in its broader asrous metal and particularly iron for the purpose pect. is thus not limited to the use of nitric acid of increasing its radiation of heat at elevated temin the preliminary treatment of the ferrous metal. peratures. but includes treatment with other oxidizing acids The carbonization of certain metals other than or agents which will leave an oxide film on the iron has been successfully practiced for some time metal and preferably will have a slight etching byheating such metals in hydrocarbon gases at action. such temperatures as to decompose the hydrocar- I shall describe by way of example the treatbon molecule and deposit free carbon upon the ment which has been proved satisfactory in car- 10 surface of the metal. Attempts to carbonize iron bonizing pure iron sheet. The sheet in the form, and other ferrous metal, however, by similar for example, of Swedish iron strip is first methods, have heretofore met with great diffi cleansed thoroughly to free its surface of oil and culty, due to the failure of the free carbon to foreign matter and is then etched in a soluuniformly deposit upon the iron and firmly adtion of nitric acid at ordinary temperature for 1 here thereto. Certain carbonizing gases which about 1% minutes time. The time may be vaoperated satisfactorily in carbonizing nickel, for ried from say minute to 3 minutes with nitric example, were found to be either entirely inoperaacid of the strength stated and at the temperative when applied to the carbonization of iron ture mentioned. Stronger solutions and higher by methods similar to those used in carbonizing temperatures will naturally require less time, and nickel, or had the great disadvantage of case any of these factors may obviousy be varied in hardening the iron to such an extent as to render accordance with well-known principles. The it unfit o many f t us s f whi h t was instrip is by this treatment etched and superficialtended. ly oxidized and thereafter it is thoroughly washed According to my present invention, ferrous in, water to remove any remaining acid The m a S Uniformly coated With firmly adherent clean oxidized and etched strip is then run C b deposit and this result y be achieved, through a carbonizing furnace at a temperature if desired, substantially without perceptible case of b t 1 F, Thi te erat re will depend hardening- In P p the invention involves somewhat on the carbonizing gas employed. the preliminary treatment of the ferrous metal s gas may b straight illuminatmg gas or under conditions which prepare its surface for the i t thereof with ther hydrocarbon onsu s qu carbonization t a d temperataining gases, but the invention in its broad sense ture i a Carbonizing 80 that the diflicult'les is not limited to a particular carbonizing gas and heretofor e cou e d are avoided- This D P- others may be substituted for those mentioned. aration of the surface has been best accomplished with any of these gases the temperature may be by treatment W nitric acid, which appears be varied within wide limits, such as for example efiec v by reason of e s ht etching of the from 1400 F. to 1300 F., athough better results' surface and the formation thereon of a thin oxide are obtained between 150m and 1750 F d film, as a result of which the carbonizing gas is in ti I prefer to keep within about 50 of decomposed and carbon set free on the surface of 16500 R temperature, where illuminatjllg gas is the metal under conditions which ensure umemployed and a, good black deposit is required 5 formlty of i coat d adherence- The The time required to obtain a satisfactory deresults obtamed are consistent wlth posit will vary somewhat with the temperature that the oxygen of the oxide film combines with and the character of the carbonizmg hydrogen of the hydrocarbon Setting free Where the strip is fed continuously through a f ch surface act i o r i wfil izs l? f a$ ;l i ?o hi adherence of carbomzmg furnace of standard deslgn the speed the deposited carbon, is further aided by the irthe strip may g be regulated y Y regularities of the etched surface in promoting of the F \IOE Secure a mamtam the adherence The if r it of the carbon desired quality of deposit. For carbonizing al- 56 posit is further consistent with the theory that ready formed sheet, such as for ex mple the the oxygen of the oxide film combines with hyplates of thermionic tubes, five or siX minutes drogen of the hydrocarbon gas, in that the forexposure to the carbonizing gas at the temperamation of the carbon deposit proceeds uniformly tures mentioned will ordinarily give satisfactory r over the exposed oxide surface and to a substanresults, but here again the observation of the re- 55 tially uniform thickness, when the deposition apsuit is the best guide to the proper regulation of the time and temperature with respect to each particular carbonizing gas.

Carbonized strip obtained by the method described may be stamped and formed into finished shapes with little or no loss of carbon from the surface, with the result that the finished object will retain satisfactory heat radiating properties, whether carbonized before or after forming.

With regard to the case hardening effect which has represented a serious difficulty in previous attempts to carbonize iron, it is found that little or no difiiculty will be encountered from this cause when carbonizing from straight illuminating gas or other mixtures; in which constituents are present such as concentration of the decomposable hydrocarbon. It is also to be noted that the case hardening effect involves a time element which is dependent upon the composition of the carbonizing gas, and in the practice of my invention, under the prin ciples explained, case hardening may readily be avoided as the deposition of the carbon is completed before case hardening has had time to develop to any appreciable extent.

As previously explainede, the broad principles of the invention are not limited to the use of specific materials or reagents, and these may acthe hydrogen and carbon monoxide of the illuminating gas to reduce the cordingly be varied by the substitution of wellknown equivalents. I have found, however, that the preliminary treatment with nitric acid as the etching and oxidizing agent, and the carbonizing with illuminating gas give particularly favorable results on pure iron, and hence the use of these is claimed as a preferred embodiment of the invention.

I claim:-

1. Method of carbonizing ferrous metal which comprises acting upon the surface with nitric acid and later exposing it to carbonizing gas at carbonizing temperature.

2. Method of carbonizing iron which comprises treating' the surface with nitric acid, and thereafter subjecting it to carbonization temperature in a gas containing carbonizable and non-Carbonizable constituents.

3. Method of carbonizing iron which comprises treating the surface with nitric acid, and thereafter subjecting it to carbonization temperature in illuminating gas.

4. Method of carbonizing substantiallt pure iron which comprises etching and oxidizing the surface with nitric acidand carbonizing it in.the presence of illuminating gas at about I600 F. to 1700 F.

JOHN H KYTIE. 

